A general printing apparatus uses a color conversion lookup table (to be abbreviated as LUT hereinafter) so as to output desired colors. The color conversion LUT includes an LUT used in calibration required to maintain a printing apparatus in a constant state, an LUT used in color matching represented by an ICC profile, and the like. In order to create such color conversion LUTs, a printing apparatus outputs patches of a plurality of colors, which are configured, as shown in, e.g., FIG. 9. Note that one square of a quadrille pattern corresponds to one patch, as denoted by reference numeral 91 in FIG. 9. By measuring these patches of a plurality of colors using a colorimeter such as a spectral colorimeter, colorimetric values are obtained, and a color conversion LUT is created by associating device-dependent values and device-independent values with each other.
Most of media used in printing contain a fluorescent whitening agent, which absorbs ultraviolet rays and emits fluorescence in the visible range (especially, in a blue-violet range) so as to increase the degree of whiteness. The fluorescent whitening effect by the fluorescent whitening agent increases/decreases depending on temperatures, as shown in FIG. 10. For this reason, the colorimetric values of printed materials output onto media including the fluorescent whitening agent also vary depending on temperatures. Variation amounts of the colorimetric values of printed materials due to the influence of the fluorescent whitening agent contained in media are largest on a medium white part, and decrease with increasing amounts of color materials such as ink and toner. That is, the variation amounts of the colorimetric values are large on a highlight part and low-saturation part where the human color perceptual sensitivity is high.
Hence, in order to manage the colors of a printing apparatus with high precision, the temperature at the time of measurement is required to be always maintained at a constant target temperature (for example, 23° C. as the standard temperature in the colorimetry field; JIS Z8703). However, this method is impractical in terms of cost. Hence, a method of predicting colorimetric values at a certain target temperature by correcting colorimetric value changes depending on temperatures is required.
As the method of correcting the colorimetric value changes depending on temperatures, the following methods are proposed.
In one method, spectral reflectance change amounts for respective wavelengths per unit temperature interval are calculated in advance for respective color samples, and the spectral reflectance at a desired temperature is predicted (for example, see patent reference 1).
In another method, change amounts of absorption coefficients and scattering coefficients in the Kubelka-Munk formula for respective wavelengths per unit temperature interval are calculated for respective color samples, and the spectral reflectance at a desired temperature is predicted (for example, see patent reference 2).    [Patent Reference 1] Japanese Patent No. 3776492    [Patent Reference 2] Japanese Patent No. 3555706
However, in the method which is described in patent reference 1 and calculates spectral reflectance change amounts for respective wavelengths per unit temperature interval, spectral reflectances for all combinations of device values that can be output by a printing apparatus cannot be predicted.
In the method which is described in patent reference 2 and calculates change amounts of absorption coefficients and scattering coefficients for respective wavelengths per unit temperature interval for respective color samples, the spectral reflectance of a mixed color can be predicted according to the mixing ratio of color samples. However, since a printed material that has undergone general halftoning has an uneven colored surface, it is also difficult for this method to predict spectral reflectances for all combinations of device values that can be output by a printing apparatus.
Since neither of the two methods consider the influence of a fluorescent whitening agent contained in substrates of color samples (printing media), they cannot appropriately correct colorimetric values for printed materials using media containing the fluorescent whitening agent.